The present invention relates to papermaking machines, and more particularly relates to a device for winding a web onto a shaft and for applying an adhesive between the web and the shaft to facilitate starting the winding process.
Production speed of tissue web is of paramount importance. Production speeds for tissue webs have leveled off in recent years. This is thought to be a result of the increasing demand for high-quality tissue and the technical difficulty of maintaining higher production speeds. At higher production speeds the tissue webs tend to vibrate and rupture due to their low basis weight and tensile strength.
Reel changing comprises switching a completed paper roll with a new, empty reel and initiating tissue web winding on the new reel. Efficient reel changing increases overall production speed by minimizing the length of downtime between reels and the number of failed reeling attempts.
A common way to initiate tissue web winding on a new reel is by threading. Threading means that a web end is pulled along through a paper or board machine by a leader. The leader consists of a strip of web which may initially be only 40 to 50 cm wide, but gradually becomes wider until it extends across the entire width of the web. The leader is cut out in the continuous web, starting either at one edge or somewhere at an optional distance from either edge of the web, whereas its length is determined by the time it takes for the tip to extend across the entire width of the web. Due to the high web speed the leader may be very long, 180 to 200 m. This incurs considerable costs for the paper mill since the cut part of the paper web must be discarded for each paper reel.
Sanitary tissue products, usually manufactured of tissue paper, are extremely market-sensitive and the quality of the product is therefore often more important than its quantity. It is thus important that during reeling the paper reel acquires several important properties, e.g., homogeneity and lack of wrinkles, tears or folds. Furthermore, high efficiency in the following conversion machines can only be achieved if the reels of paper from the paper machine have a homogenous high quality.
Soft paper with low strength must be reeled carefully in order to keep the paper qualities such as density and elasticity as constant as possible throughout the reel. The two main factors affecting reel density are web tension and radial pressure at the nip of the reel-up. Lower nip pressure is important to obtain lower average density.
The thickness and elasticity of the web decreases from the outside of the reel to the center in a radial direction. This is because the compressive stress is built up in the paper reel during reeling and compresses the inner radial parts of the reel. This causes a decrease in thickness of the inner web layers. This effect increases if the reel is stored for too long before being rewound or converted.
Reeling problems arise when a new reel of paper is commenced with the aid of the tapered leader as mentioned above, since the web turns applied during winding of the innermost layers produce an uneven radial growth axially along the reel shaft so that the reel becomes carrot shaped. This is caused partly by the superelevation of the web and partly by differences in the nip pressure across the web.
If the cross-sectional profile of the paper web differs with regard to thickness, web tension or elasticity then pleating, crushing damage, defects in web and axial forces in the reel will occur at a high nip pressure. This may, in worst cases, result in web rupture. Eliminating the incidence of the carrot shaped reel, high nip pressure and web rupture could be accomplished with an apparatus for full-width reel changing. Changing xe2x80x9cfull-widthxe2x80x9d reels in the present context refers to wrapping the entire width of the web around the reel shaft when initiating a new reeling operation. This is to be distinguished from threading using a tapered leader.
High web speed machines use either the threaded or full-width methods and must wrap the web around the empty reel shaft. At high web speeds, glue is applied to the leader itself before it is threaded. At low speeds, such as those used for tissue paper production, full-width methods assisted by balloon blowing are common. Balloon blowing entails creating slack across the full width of the web by somewhat retarding the finished reel. With the aid of compressed air, the fold thus formed is then forced into the nip between the new reel shaft and the reel drum, after which the web is cut off. In order to increase the reliability of this type of reel switching, glue or tape is also applied, but only on the actual reel shaft before this comes into contact with the paper web.
Many methods of glue or adhesive application have been used such as manual application using a large brush or spray gun. Regardless of the transfer method used for switching reels, it is important that the glue is still adhesive when contact occurs between the paper web and reel shaft. It is thus desirable to use simultaneous glue spraying as opposed to manual methods.
Automatic glue spraying is accomplished with the aid of glue nozzles, generally placed at one side of the paper web, close to the primary arms. However, when applying the glue by means of spraying, great care must be taken to avoid the glue being misdirected. In earlier attempts at full-width reel switching considerable problems have been encountered with the use of spray pipes across the machine direction. The glue from spray pipes tends to drip onto the paper web below, causing the web layers to adhere to each other and the web to be torn during rewinding.
The use of aerosol jets for glue application avoids some of the problems of dripping as is demonstrated by U.S. Pat. No. 6,045,085. This invention mixes compressed air of predetermined amounts with the conventional liquid glue or adhesive as it exits a nozzle. The nozzle is actually one nozzle inside another, one of which sprays the compressed air and the other the liquid glue. The glue is distributed in a flat and wide fish tail pattern by several of the nozzles arranged side-by-side on a screen mounted upstream of the paper reel. The consistency of the aerosol spray avoids some of the dripping problems encountered with the spray pipes. However, glue and dust still have a tendency to collect on the tips of the nozzles, which sometimes results in dripping.
European Patent Application EP 0 931 744 A2 discloses a reel-changing method that involves spraying glue directly onto the sleeve of the core. However, the conventional glues used in both of the documents can clog the gluing apparatus because they tend to harden when they dry, and then require dissolving with a suitable solvent in order to free the clogs. The invention taught by U.S. Pat. No. 6,045,085 uses a needle apparatus to address the problems of glue clogging at the nozzles, but the needle doesn""t always clear the nozzles efficiently and the nozzles may still become plugged with glue. Also, the glue must be continuously circulated in the conduits supplying the nozzles to reduce the incidence of clogging. This increases the weight of the equipment that must be supported by a spray rack or screen. The viscosity of the glue can be decreased by dilution, but then the glue loses much of its stickiness.
Therefore, it would be advantageous to automatically apply an adhesive between the web and the reel shaft on which it is wound for full-width reel switching, such that the adhesive can be applied evenly, in a very controlled area and without problems of dripping or clogging. Also, it is important that the glue remain sticky after application, while being flowable so that it can be easily applied.
The apparatus and method according to the invention meets these and other needs and is characterized by a rotatable reel drum supporting a web wrapped partially about the reel drum. The apparatus includes a winding device for supporting and rotating the reel shaft about its axis. At least one of the reel drum and the winding device for supporting the reel shaft is movable toward the other to place the rotating reel shaft in a winding position proximate the reel drum such that the web on the surface of the reel drum is engaged by the rotating reel shaft. A plurality of spray nozzles are operable to spray an adhesive and are located to spray the adhesive on either the web, or the outer surface of the reel shaft, or both. The plurality of spray nozzles can be located in various mounting positions such as near the web upstream of the reel drum, at the nip between the reel shaft and reel drum, or directly onto the reel shaft. The spray nozzles can also be located to spray on the reel shaft as it is lowered from a stock of empty reel shafts by a lowering arm into the position proximate the reel drum, by fixing the nozzles to the frame of the winding device, or to the lowering arms in a reel-up having such arms.
Application of the adhesive on the web and/or reel shaft allows the web to adhere to, and begin winding about, the reel shaft as it is brought into engagement with the web on the reel drum. An adhesive supply apparatus includes a tank, at least one conduit and a driving unit. The driving unit includes a piston, a pump, compressed air or other means for delivery of the adhesive from the tank to the nozzle and to spray the adhesive out. In accordance with the invention, the adhesive is characterized by a viscosity that becomes lower upon the heating of the adhesive. Thus, no dilution of the adhesive is needed in order to render it flowable. Instead, the adhesive is heated to a temperature sufficient to reduce the adhesive viscosity to a level at which the adhesive can be readily sprayed from the nozzles. The tank thus preferably comprises a heater and holds the adhesive, which is heated by the heater to render the adhesive flowable. The adhesive could be solid or liquid, but is preferably a semi-solid, or is gel-like and is also water soluble. The conduit connects the tank with the spray nozzles and the driving unit delivers the flowable adhesive through the conduit to the spray nozzles. The adhesive is preferably heated all the way to the nozzles only enough to reduce the viscosity sufficiently to allow the adhesive to be delivered more easily through the conduits to the nozzles. Even if the adhesive solidifies upon cooling, such as during a shut-down of the winding apparatus, clogs can be easily cleared by heating the adhesive in the system.